1. Field of the Invention
The present invention relates to a thermal head used for a thermal printer, and particularly relates to an improvement of a wear-proof layer of the same.
2. Description of the Prior Art
A thermal head to be mounted in a thermal printer is arranged such that, for example, a plurality of heat-generating resistor elements are linearly arranged on one and the same substrate so that the resistor elements are selectively energized in accordance with information to make thermo-sensitive recording paper color to thereby record the information on the paper, or to transfer the information onto ordinary paper through an ink ribbon to record the information on the paper.
Conventionally, as shown in FIG. 4, a thermal head has been manufactured by successively laminating a heat-generating resistor layer 3 including Ta.sub.2 N, a power supply conductor layer 4 including, Al, Ni, and so on, an oxidation-proof layer 5 including SiO.sub.2, and a wear-proof layer 6 including Ta.sub.2 O.sub.5, one by one on an electrically insulating substrate 1 of, for example, alumina or the like on which a glass glaze layer 2 is partially formed. In this case, the power supply conductor layer 4 is patterned to be constituted by a plurality of individual electrodes and a common electrode to form a heat-generating portion A between the common electrode and the respective individual electrode.
Recently, the thermal head has been required to be able to make record even on rough paper, to be able to make record at a high speed, to be able to be driven also by a battery, and so on. In order to realize those requirements, it is demanded to make the thermal conductivity of the heat generating portion good to thereby make the thermal efficiency high.
In the conventional thermal head, however, the wear-proof layer is a homogeneous layer including Ta.sub.2 O.sub.5, so that heat is conducted isotropically and escapes in the transversal direction. Further, the material per se of the wear-proof layer is low in thermal conductivity. Therefore, it has not been possible to make the thermal efficiency of the thermal head sufficiently high.